FIGS. 1 and 2 are cross-sectional views of a conventional spotlight assembly. Lamp 6, which is a type of lamp known as a "Par-64", is connected to one end of a hollow "ParCan" housing 4. A light beam 5 passes from lamp 6 along optical axis OA through housing 4 and intercepts a plane-of-media Pm normal to axis OA. The region around plane Pm is commonly used for holding light filters or other optical elements (not shown in FIG. 1).
Lamp 6 has a clear cover glass 9. FIG. 2 shows a lamp 7 which is similar to lamp 6 but has a diffuser 9d which provides a wider beam. Lamps 6 and 7 are sealed-beam units which have to be replaced when they are worn out or when a different beam size is desired.
An improvement over lamps 6 and 7 is described in U.S. Pat. No. 4,855,884, which is assigned to the assignee of the present invention and which is incorporated herein by reference. The stage light therein described contains a reflector which is adjustable so as to vary the width of the beam produced by the light. The reflector and housing are permanent and need not be replaced when the light bulb is worn out. When the reflector is adjusted to a state of minimal curvature (shown in FIG. 2A of U.S. Pat. No. 4,855,884) the light rays are emitted in a substantially parallel pattern, as shown in FIG. 1 hereof. As the curvature of the reflector is increased through a range of tighter, elliptical shapes, a configuration such as is shown in FIG. 3 is produced. Elliptical reflectors have the characteristics of reflecting light from one focal point to a second focal point. Thus, as shown in FIG. 3, rays emanating from a first elliptical focal point Fl are reflected to a second elliptical focal point F2 where they cross and diverge.
When the light beam is focused in this way, a temperature extreme is created at point F2. As FIG. 3 shows, in a worst case this temperature extreme can coincide with plane Pm, where light filters or other optical elements may be located. If gelatin or plastic filter media susceptible to high temperature are positioned at or near plane Pm, then those media may fade, deteriorate, or possibly melt.
Accordingly, there is a need for a device which will avoid the extremely high temperatures which can be generated when a lamp such as the improved lamp described in U.S. Pat. No. 4,855,884 produces the convergence of light rays illustrated in FIG. 3.